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1.
A magnesium/electron donor complex was used as support for the synthesis of a titanium catalyst. By interaction of TiCl4 with MgCl2(THF)2 a highly active and stable catalyst for ethylene polymerization was obtained. The catalytic activity of the MgCl2(THF)2/TiCl4/AlEt2Cl system in the polymerization of ethylene was investigated as a function of Mg/Ti and Al/Ti mole ratios as well as the donor concentration in the system. Some kinetic studies of ethylene polymerization in the presence of this catalyst allowed us to determine the concentration of active centres (ca. 60 mol-% of Ti), rate constants of elementary reactions (kp ≈ 92 dm3/(mol · s)) and kinetic equations. From these results it was possible to find further evidence for the role of the donor ligands in titanium catalysts supported on magnesium dichloride in the presence of Al-alkyls as cocatalysts. 相似文献
2.
Luiz Claudio de Santa Maria Kazuo Soga Takeshi Shiono 《Macromolecular chemistry and physics.》1994,195(7):2591-2598
MgCl2/TiCl4/SiO2 catalysts were prepared by treating TiCl4/SiO2 with MgCl2 · 2THF (THF: tetrahydrofuran) at different Mg/Ti ratios. The catalysts were analysed by X-ray, electron spin resonance (ESR), atomic absorption spectrometry to determine the crystal structure, oxidation state of titanium and also contents of Ti, Al and Mg. Homo- and copolymerizations of ethylene and propene were conducted with them using Al(i-C4H9)3 as a cocatalyst. The results of polymerization were correlated with the analytical data of the catalyst. 相似文献
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John C. Chadwick Giampiero Morini Enrico Albizzati Giulio Balbontin Ines Mingozzi Antonio Cristofori Olof Sudmeijer Gerard M. M. Van Kessel 《Macromolecular chemistry and physics.》1996,197(8):2501-2510
13C NMR analysis of the chain-end distribution of poly(propylenes) prepared using the highly active catalyst system MgCl2/TiCl4/diether—AlEt3 has revealed particularly high proportions of butyl chain-ends in polymers prepared at relatively low hydrogen pressures. This indicates that the high sensitivity of this type of catalyst to hydrogen, both with respect to catalyst activity and polymer molecular weight, can largely be ascribed to chain transfer following regioirregular (2,1-) insertion, such an insertion leading to a species having low activity in chain propagation. Isotactic stereoregularity increases with increasing hydrogen pressure, indicating that a stereoirregular insertion may also slow down the chain propagation, again leading to chain transfer and resulting in the conversion of a potential chain defect into an isobutyl chain-end. Analysis of highly isotactic polymer fractions isolated via temperature rising elution fractionation revealed the presence of both butyl and isobutyl chain-ends, indicating that even the most highly stereo-specific sites in MgCl2-supported catalysts are not totally regiospecific. 相似文献
5.
Zhikang Xu Lingxiang Feng Dongli Wang Shiling Yang 《Macromolecular chemistry and physics.》1991,192(8):1835-1840
Copolymerization of propylene 1 System name: propene. and 1-alkenes (1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene) were studied with the catalyst system MgCl2/TiCl4-Al(i-Bu)3. It was found that the polymerization productivity and the consumption rate of propylene are improved significantly in the presence of the comonomer. The total productivity of propylene/1-alkene copolymerizations decreases as follows: 1-octene > 1-decene > 1-dodecene > 1-hexadecene > 1-tetradecene. The reactivity ratios were estimated from the copolymerization results. 相似文献
6.
Alexandr G. Potapov Vladimir V. Kriventsov Dmitrii I. Kochubey Gennadii D. Bukatov Vladimir A. Zakharov 《Macromolecular chemistry and physics.》1997,198(11):3477-3484
Extended X-ray absorption fine structure analysis (EXAFS) has been used to study supported TiCl4/MgCl2 catalysts containing 1.8 wt.-% Ti. Adsorbed TiCl4 was found to exist on the MgCl2 surface as a dimeric complex. The possible structures of dimeric TiCl4 complexes on the (100) face of MgCl2 are discussed. 相似文献
7.
Temperature effect of TiCl4 impregnation of a recrystallized MgCl2 support on propene polymerization
Ho Woo Shin Jin Suk Chung In Kyu Song Wha Young Lee 《Macromolecular chemistry and physics.》1995,196(11):3765-3770
The MgCl2 support for a propene polymerization catalyst was prepared by the recrystallization method using ethanol as a solvent and ethyl benzoate as an internal electron donor. The recrystallized MgCl2 was impregnated with TiCl4 at various temperatures, and the effect of impregnation temperature on the catalytic activity and isotactic index (I. I.) of polypropene (PP) was investigated. It was found that ethanol and titanium chloride ethoxide (TCE) in the catalyst play an important role in the catalytic activity and I. I. The support treated with TiCl4 at high temperatures showed good performance but large activity reduction during polymerization. The enhanced performance is mainly due to activity Ti species containing small amounts of TCE. The large activity reduction is also mainly due to small amounts of ethanol and TCE, yielding small amounts of atactic sites with low Lewis acidity. 相似文献
8.
Jukka V. Seppl Mika Hrknen Luciano Luciani 《Macromolecular chemistry and physics.》1989,190(10):2535-2550
Propene was polymerized in bulk in the presence of high activity heterogeneous Ziegler-Natta catalyst with the purpose of finding correlations between the structure of an external alkoxysilane donor and the polymer. Nineteen silane compounds ( 1–8 ) of the structure RnSi(OR′)4-n, where n = 1–4, R°C6H5, alkyl or H; R′ = C1–3-alkyl, were used as external donors. The effect of Si/Al mole ratio was studied. The effect of the external alkoxysilane donor on the polymerization strongly depends on the number and size of alkoxy groups and the size of hydrocarbon groups attached to the silicon atom. Two major effects were observed: selective deactivation of atactic active centers and the increased production of high-molecular-weight isotactic polypropylene. Evidently, at least one free non-hindered alkoxy group in the complex between alkoxysilane and AlEt3 is required for the selective deactivation. Also, the size of the hydrocarbon group of the donor strongly influences the selectivity of the deactivation. 相似文献
9.
A good supporting material for Ziegler-Natta type catalysts was obtained by reaction between powdered metallic magnesium and 1-chloro-n-CmH2m+1 (m = 3–9). This reaction affords a highly disordered form of MgCl2 which was characterized by FT-IR spectroscopy and powder X-ray diffraction (XRD) analysis. This MgCl2 form shows a crystallographic disorder much higher than that exhibited by the products obtained following the commercial activation procedures of α-MgCl2, either mechanical or chemical. As shown by the XRD spectra, the synthetized MgCl2 is characterized by the typical structure of the δ-form. Therefore, this MgCl2 form, in view of its highly disordered structure, appears as a promising material for the preparation of active supported Ziegler-Natta type catalysts. Thus, by titanation of the obtained δ-MgCl2 we have prepared some supported catalysts which have been tested in the slurry propene polymerizations, showing high activity (136000–138000 gPP/gTi) and good stereoselectivity (82–88% I.I.). 相似文献
10.
Giuliano Cecchin Enzo Marchetti Giovanni Baruzzi 《Macromolecular chemistry and physics.》2001,202(10):1987-1994
A morphological investigation was carried out on spherical catalysts based on MgCl2‐supported TiCl4 and related nascent polymer particles, including both homopolypropene and polypropene‐based multiphase copolymers. Transmission and scanning electron microscopy show that both catalyst and polymer grains display a dual morphological texture consisting, respectively, of microparticles and subparticles (catalyst) and microglobules and subglobules (polymer). The morphology of sequential, multiphase copolymers indicates that the second monomer, either ethylene or 1‐butene, or monomer mixture, ethylene/propene, polymerizes around the pre‐formed subglobules of the homopolypropene matrix. Based on the experimental results, a model/mechanism of polypropene growth has been proposed that entails the features of both a dual grain and a polymeric flow system: the monomer polymerizes at the surface of catalyst microparticles forming a polymer shell (microglobule) around each of them; polymer microglobules form larger agglomerates (subglobules) which, as polymerization goes on, tend to behave as individual polymeric flow units: catalyst microparticles undergo further fragmentation and tend to be convected from the bulk to the surface of polymer subglobules, where they sustain the reaction. 相似文献
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Takeshi Shiono Masaaki Ohgizawa Kazuo Soga 《Macromolecular chemistry and physics.》1993,194(7):2075-2085
The reaction between carbon monoxide and the Ti-polyethylene bond was investigated by using a stopped-flow polymerization method which can provide quasi-living polymers with very low molecular weights. Ethylene polymerization was conducted with a typical MgCl2-supported TiCl4 catalyst combined with triisobutylaluminium (Al(i-C4H9)3) or Al(CH3)3. The quasi-living polymers were introduced into either the heptane solution saturated with carbon monoxide or the heptane solution containing 13C-enriched carbon monoxide at ?78°C. The mixture was gradually heated up to room temperature. During this procedure, a small portion of the reaction mixture was taken out at ?78°C, 0°C and at room temperature. The polymers produced were analyzed by means of Fourier-transform infrared spectroscopy, gel-permeation chromatography, proton nuclear magnetic resonance (1H NMR) and 13C NMR spectroscopy. The analytical data show that carbon monoxide is predominantly incorporated into the polymers as a ketonic carbonyl. 相似文献
14.
Polymerization of propene with a highly isospecific Solvay-type TiCl3/Cp2TiMe2 catalyst in the presence and absence of hydrogen was investigated. It was found that hydrogen exerts almost no effect on the molecular weight and the stereoregularity of the resulting polypropylene. Furthermore, the H2/D2 exchange reaction hardly proceeds over the catalyst. To discuss this unusual behavior, plausible mechanistic explanations on the basis of the structure of active species are proposed. 相似文献
15.
Daniele Fregonese Vito Di Noto Arnaldo Peloso Silvano Bresadola 《Macromolecular chemistry and physics.》1999,200(9):2122-2126
The effects of triethers as internal donors on the activity and stereoselectivity of MgCl2-supported Ziegler-Natta type catalysts in the propylene polymerization were studied. In particular, we prepared and fully characterized some procatalysts of the type δ-MgCl2/ID/TiCl4, where ID are internal donors such as di(ethyleneglycol) diethyl ether (DEGDEE) and di(ethyleneglycol) dimethyl ether (DEGDME). By aging these procatalysts with AlEt3 (cocatalyst) we obtained δ-MgCl2/ID/TiCl4/AlEt3 catalytic systems, which were tested in the propylene polymerization in order to evaluate their catalytic performance. All polymerizations were carried out in the absence of both external donors (ED) and hydrogen. The productivity and the properties (Mw, Mn, Mw/Mn, and isotacticity index (I.I.)) of the polymers obtained were determined and the results compared with those obtained by using catalysts either lacking an internal donor or with ethyl benzoate as internal donor. The comparison pointed out that the presence of triethers lowers the productivity of the catalysts and increases their stereoselectivity. Polydispersity is also remarkably enhanced suggesting that a multiplicity of active catalytic sites characterized by different environments is present. 相似文献
16.
Copolymerization of propylene with 1-butene in presence of the catalytic system TiCl4/Mg[(CH2)5CH3]2
Kazuo Soga Makoto Ohtake Rikuo Ohnishi Yoshiharu Doi 《Macromolecular chemistry and physics.》1985,186(6):1129-1134
The copolymerization of propylene with 1-butene was carried out in presence of the catalytic system TiCl4/Mg[(CH2)5CH3]2 in heptane. A transparent copolymer with a random distribution (r1 · r2 = 1,0) was obtained. The catalyst shows a considerably high activity. The rate of monomer addition was found to be independent of the chemical structure of the growing polymer chain end, which is quite different for the copolymerization of ethylene with propylene. 相似文献
17.
Isam A. Jaber Klaus Hauschild Gerhard Fink 《Macromolecular chemistry and physics.》1990,191(9):2067-2076
The determination of active centres concentration in ethylene polymerization using various TiCl4/MgH2-Al(C2H5)3 catalytic systems, by the 14CO radio-tagging method, is reported. It is found that with increasing the absolute titanium amount the concentration of active centres, [C*], increases, whereas the propagation rate constant, kp, decreases. In addition, using various TiCl4/MgH2 catalysts in ethylene polymerization, it is found that the lower the Ti content, the higher is the surface area of the catalyst and the higher is the polymerization activity. Determination of [C*] shows consclusively that the decrease in the polymerization activity observed to occur with increasing the Ti content, and thus decreasing the surface area, is unequivocally due to a reduction in the concentration of active centres but not to any fundamental change in the value of the propagation rate constant. 相似文献
18.
Maria Carmela Sacchi Zhi-Qiang Fan Fabrizio Forlini Incoronata Tritto Paolo Locatelli 《Macromolecular chemistry and physics.》1994,195(8):2805-2816
The effects of different alkoxysilane donors (Ph(EtO)3Si, Me(EtO)3Si and Ph2(EtO)2Si) have been compared in propene/1-butene copolymerization with MgCl2-supported Ziegler-Natta catalysts. The copolymers obtained were fractionated and the fractions characterized by 13C NMR analysis. The influence of the different alkoxysilanes on the yield, the fraction distribution and the composition, the reactivity ratios and the number-average sequence lengths of all the fractions were analyzed. The results obtained show that it is possible to vary the characteristics of propene/1-butene copolymers by varying the bulkiness of the hydrocarbon substituent and/or the number of the alkoxy groups of the silane donor. It was also possible to correlate the effect of the silane donor on the homopolymerization stereochemistry and on the characteristics of the copolymers. 相似文献
19.
Kazuo Soga Masa-aki Ohgizawa Takeshi Shiono 《Macromolecular chemistry and physics.》1993,194(8):2173-2181
Copolymerization of ethylene with a small amount of propene was conducted with a TiCl4/MgCl2-Al(C2H5)3 catalyst system using a stopped-flow method. With an increase in the polymerization time from 0,035 to 0,145 s, the copolymer yield increases linearly but the number-average molecular weight of the copolymer showed a tendency of saturation. The rate constants of the propagation reaction as well as the concentrations of active sites were estimated using these data. On the other hand, the 1H NMR spectra of copolymer did not display the resonances due to C?C double bonds which should be formed by chain transfer with monomer and/or by β-hydrogen elimination. It was also found that the crystallinity of the copolymer decreases to a great extent upon incorporation of even a very small quantity of propylene units. From these results, it was concluded that the apparent rate of copolymerization is not controlled by monomer diffusion through the polymer films. Rather the transfer reaction with Al(C2H5)3 might predominantly take place during the copolymerization. 相似文献
20.
Synthesis of Ultrahigh Molecular Weight Polyethylene Using MgO/MgCl2/TiCl4 Core–Shell Catalysts
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Yusuke Bando Patchanee Chammingkwan Minoru Terano Toshiaki Taniike 《Macromolecular chemistry and physics.》2018,219(10)
In this study, MgO/MgCl2/TiCl4 core–shell catalysts are employed for the production of ultrahigh molecular weight polyethylene (UHMWPE) particles, motivated by their advantages including simple preparation, ease of morphology control, and a dramatically reduced Cl content. It is found that the MgO/MgCl2/TiCl4 core–shell catalysts can provide UHMWPE at a reasonable activity, but the agglomeration of the catalyst particles leads to poor morphology of the UHMWPE. The dispersion problem is largely alleviated by modifying MgO nanoparticles with methyl oleate (MO). Thus, the MO‐modified MgO/MgCl2/TiCl4 core–shell catalyst successfully affords UHMWPE particles of 100–200 µm at a high yield of 8670 g‐PE g‐Cat?1. 相似文献